This disclosure is directed to a method and apparatus for automatically controlling the production of pitch-like materials which have viscosity as an important characterization value. More particularly, the invention is directed to a method and apparatus for automatically controlling the production of pitch and the like by simultaneously measuring the viscosity and temperature of the pitch material, comparing this measured correlation with a predetermined correlation of the viscosity and temperature for the pitch material and adjusting the parameters of the pitch process in response thereto.
Coal tar pitches and petroleum based pitches have found wide use in various industries. They have been used for many years as waterproofing agents and protective coatings. Some examples of these uses include built-up roofings, foundation wall coatings, pipeline enamels, and many others. The pitches are usually applied in these uses as a hot melt. Some other important uses of pitches is as binders for paving materials, binders for electrodes for the aluminum and steel industries and as binders for a great variety of carbon products.
Each tar pitch as well defined characteristics and properties which are dictated generally by the end use which they are designed to serve. Normal tar pitches usually have softening points of at least about 40.degree. C and this may be as high as 135.degree. C or higher.
The pitches of different softening points are generally prepared by subjecting the crude tar pitches to a heat treatment or to a heat treatment in combination with various chemical reactants such as oxygen or air. The most common method of preparing pitches of different softening points is distillation.
Heretofore, the production of pitches having different softening points was controlled by a totally manual process. After selection of a suitable tar source and distillation conditions (temperature and pressure) continuous pitch still operations are controlled by the softening point of the pitch product. In general, a customer specifies a certain softening point (by the ring and ball or similar method) with a latitude of plus or minus 10.degree. C. The still operator adjusts the controls according to the desired softening of the product. This involves taking a sample from the reactor, preparing it for the softening point determination, carrying out the latter, comparing the softening point to the desired softening point, and adjusting the controls according to the comparison value. It takes from about 30 minutes to one hour to take the softening point, make the comparison and adjust the controls. After adjustments, it takes at least another half hour or so before the reaction mixture comes to equilibrium and another sample can be taken. Because of the inherent difficulties with the prior art method, there has been a desire in the industry for a better method and apparatus for controlling pitch still operations.